1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which a pair of substrates sandwiching a liquid crystal is bonded together by a sealing material for sealing the liquid crystal.
2. Description of the Related Art
Liquid crystal display devices (liquid crystal display panels) have a structure in which a pair of substrates arranged so as to be opposed to each other for sandwiching a liquid crystal serves as an envelope, an image display portion including an aggregation of multiple pixels is located in a direction in which the liquid crystal spreads, and the liquid crystal is sealed by a sealing material provided between the pair of substrates to surround the image display portion.
In this case, enhancing the substrate-side adhesion of the sealing material improves the sealing effect of the sealing material, and a reliable liquid crystal display device is obtained as a result.
In some cases, this structure has a black matrix (herein, sometime referred to as light-shielding film in this description) formed on the liquid crystal side of one of the paired substrates. The black matrix has an opening in each pixel region in the image display portion to provide an effect of blocking light between adjacent pixels, thereby attaining an improvement of the contrast.
In this case, the black matrix is structured to extend to an outside of the image display portion until the black matrix overlaps well with a region where the sealing material is provided (hereinafter, referred to as sealing material formation region), thereby blocking light in the periphery of the image display portion. This prevents light leakage caused by, for example, light emitted from a backlight, which is provided on the rear side of the liquid crystal display panel, and transmitted through the sealing material and its vicinity.
An example of technology related to the black matrix under a sealing material is disclosed in JP 2008-176237 A, where a part of the black matrix that overlaps with the sealing material has a slit or an opening. This black matrix is coated with an overcoat film made of a resin, and is improved in adhesive strength because the substrate is brought into contact with the overcoat film in the slit or opening, which means a larger bonding area is obtained between the substrate and the overcoat film.
Other documents relevant to the present invention include JP 2008-107488 A and JP 2007-304273 A. JP 2008-107488 A discloses a black matrix with a slit in a place where the black matrix overlaps with a photo-curing sealing material. This document mentions that, in curing the sealing material after a light-shielding wiring pattern is formed on the other substrate, which is not the one where the black matrix is formed, such that the wiring pattern overlaps with the sealing material, the sealing material is irradiated with light through the slit formed in the black matrix. JP 2007-304273 A discloses a black matrix with a slit in a place where the black matrix overlaps with a photo-curing sealing material. This document does not mention a wiring pattern that is arranged to overlap with the sealing material as the one in JP 2008-107488 A, but describes the irradiation of the sealing material with enough light through the slit formed in the black matrix.
In some liquid crystal display devices, an insulating film or the like formed in the image display portion on the liquid crystal side of each of the paired substrates is, for example, in multiple layers and extends to the sealing material formation region.
JP 2007-256415 A, JP 2007-199341 A, and JP 2007-248743 A, for example, disclose structures of the insulating film or the like formed on the liquid crystal side of each substrate that are designed to improve the substrate-side adhesion of the sealing material.
Specifically, JP 2007-256415 A discloses a structure in which the insulating film or the like is a laminate of a gate insulating film and an organic insulating film which are formed in order on the substrate, and the organic insulating film has a through hole that exposes a surface of the gate insulating film in the sealing material formation region. The sealing material is thus bonded to the gate insulating film as well through the through hole formed in the organic insulating film.
In addition, JP 2007-199341 A discloses a structure in which the insulating film or the like is a resin film formed on the substrate, and the resin film has a through hole that exposes a surface of the substrate in the sealing material formation region. The sealing material is thus bonded to the substrate through the through hole formed in the resin film.
Further, JP 2007-248743 A discloses a structure in which an inorganic alignment film formed on the substrate with an insulating film interposed there between extends to partially overlap with the sealing material formation region. The sealing material adheres better with the inorganic alignment film than with the insulating film, and hence the adhesion is accordingly improved. Further, leaving part of the sealing material formation region free of the inorganic alignment film has an additional effect of creating a level difference from the inorganic alignment film which reduces the infiltration of moisture.